Recess plates are commonly known, inter alia from DE 10 2007 027 033 A1. Recess plates must be capable to take unavoidable differential pressure, and to return back to original shape after deflection due to differential pressures. They must take huge closing and sealing forces and full process pressures, without being compressed. Machining must be possible to ensure dimensional accuracy, and installing sealing rings and membranes. Fixing and supporting areas must be sufficiently strong, and they must provide opportunity to include internal channels for filtrate, washing media, air etc. These days, such recess plates are mostly molded from polypropylene (PP), or even from steel, and subsequently machined to the final shape.
Both the limited number of PP plate manufacturers and limited size of molding presses technically and economically constrains both manufacturing and application of filter devices.
US 2001/0021428 A1 suggests a method according to the above, wherein a shell including the first and second sheets is manufactured as one sealed hollow piece from rigid polyethylene by rotational moulding.